An AlN (aluminum nitride) crystal has a wide energy band gap of 6.2 eV, a high thermal conductivity of about 3.3 WK−1 cm−1, and a high electrical resistance. Thus, nitride crystals such as an MN crystal have been attracting attention as materials for semiconductor devices such as optical devices and electronic devices.
A method of manufacturing such a nitride crystal is disclosed, for example, in Japanese Patent Laying-Open No. 2007-197276 (Patent Document 1). In Patent Document 1, a group III-V nitride semiconductor substrate is manufactured by the following steps. Specifically, a group III-V nitride semiconductor film is grown on a substrate of a different type having a c-plane or an off angle. Thereafter, a metal film is deposited on the substrate of a different type, and heat treatment is performed to form cavities in the group nitride semiconductor film. Next, a group III-V nitride semiconductor crystal is deposited on the metal film. Subsequently, the substrate of a different type is delaminated to obtain a group III-V compound semiconductor crystal having a c-axis substantially vertical to a front surface or inclined by a predetermined angle with respect to the front surface. Next, a rear surface of the group III-V nitride semiconductor crystal is polished to obtain a flat surface. A group nitride semiconductor substrate is manufactured by removing the substrate of a different type, the group III-V nitride semiconductor film, and the metal film from the group III-V nitride semiconductor crystal. A semiconductor substrate made of the group III-V nitride semiconductor crystal manufactured as described above has an as-grown front surface.